1. Field of Invention
This invention relates generally to methods for transporting webs through a conditioning zone, wherein the web pursues a sinusoidal path; the invention also relates generally to an apparatus wherein a moving web is caused to pursue a sinusoidal path between a plurality of nozzles; and particularly, the invention relates to rectangular orifices discharging supporting jets of air over a convex indentation generally tangential to an arcuate surface on the nozzle, sustaining the web by the Coanda Effect; and circular orifices discharging jets of air generally perpendicular to the convex face of a nozzle.
2. Prior Art
In the art of printing or coating paper, fabrics or metal strips, the print or coat must be allowed to dry before the imprinted web can be rolled-up, in order to prevent smudging or marring of the design or coat. Resort to rapid drying coatings or inks does not provide a solution for the problem, because the ink or coat takes time to dry, and the roll-up can only proceed as slowly as the ink or coat dries. The passing of the web through a heated atmosphere is a common expedient, but the web must be sustained as it goes through the drying chamber, otherwise, it may not dry uniformly, or it may, while still wet, contact the interior portions of the chamber or nozzles, and have its coat or design scraped or marred. Thus various chambers for drying have been devised, having many nozzles on both sides of the course over which the web is intended to pass, but these nozzles are not always successful in preventing the moving web from fluttering, wrinkling, or scraping against the nozzle; all of these devices pursue the objective of having the web pursue a precise linear course. To attain this objective, many new nozzles have been devised, e.g. Wallin: U.S. Pat. No. 3,231,165; Schregenberger: U.S. Pat. No. 3,837,551; Frost: U.S. Pat. No. 3,549,070. The nozzles of these devices are able to float lightly coated light, flexible webs with very little contact that may impair the coating or design imprinted, but when it comes to floating webs with rough or sticky coatings, particularly when the webs are of very light material, the webs often wrinkle, flutter and touch the nozzles, so that the design or coat is impaired and the marred portion of the web becomes useless and must be discarded. Eyelid-type air-jet openings may cause dimples in the web, tending to create tension of the web, that results in vibration and fluttering with striping of the coat. When the eye-lid type nozzles are arranged in staggered array, the web edges may flutter. The force of the air discharged may cause portions of the designs to run, splash, or stripe, further marring and impairing the design.
3. Definition
Coanda Effect as referred to herein means the tendency of a gas stream filament to follow the wall contour when discharged adjacent to a surface, and particularly when that surface curves away from the discharge axis of the air stream filament.